FIG. 12 is a diagram showing a conventional radio equipment. In the diagram, the reference numeral 1 designates a host controller; 2, a radio module; 3, a base band controller; 4, an endless interface; 5, a power amplifier; 6, a low-noise input amplifier; 7, a switch; and 9, an antenna as an inverted F antenna.
In the diagram, the host controller 1 transfers data to the base band controller 3. The base band controller 3 modulates the transferred data. The modulated electric signal is amplified by the output amplifier 5 and radiated as a radio wave from the antenna 9 to space through the switch 7. On the other hand, a radio wave propagated through the space is received in the antenna 9 and amplified by the low-noise input amplifier 6 through the switch 7. Then, the amplified electric signal is demodulated to data by the base band controller 3 and transferred to the host controller 1.
In the conventional radio equipment, because the output of the power amplifier 5 and the input sensitivity of the low-noise input amplifier 6 are fixed, the radio coverage range and the input receiver coverage in the radio equipment are also fixed. Accordingly, when, for example, a user of one radio equipment in which both coverage range and input receiver coverage are 10 m wants to communicate with another radio equipment having equal performance, the user (or the radio equipment itself) can judge whether the other radio equipment is in an area with a 10 m radius centering about the user or not.
The user of the radio equipment cannot judge whether any other radio equipment is near the user in the area with a 10 m radius. In other words, the user cannot specify who is the other radio equipment existing near the radio equipment of the user himself/herself. Furthermore, the user of the radio equipment cannot confirm whether the other radio equipment is coming near to or going far away from the user himself/herself.
On the other hand, there is a radio equipment in which the output of the power amplifier 5 is variable. In the radio equipment, however, the ratio of output to input sensitivity varies, so that the radio coverage range depending on the output is not equal to the input receiver coverage of the radio wave depending on the input sensitivity.
When, for example, the output of a radio equipment used as a base station at a certain point of time is raised, electric field intensity around the base station becomes so high that the coverage range is widened. Accordingly, a radio wave from the base station is audible to any radio equipment existing within the widened coverage range. When the base station calls any ambient radio equipment in this state, the ambient radio equipment tries to reply to the base station but linkage to the base station cannot be established because the output of the ambient radio equipment is low yet. Furthermore, there is a disadvantage that normal communication is disabled because the ambient radio equipment does nothing but repeat replying.
When the output of a radio equipment used as a mobile station at a certain point of time is lowered, electric field intensity around the mobile station is reduced so that the radio coverage range is narrowed. Accordingly, a radio wave cannot reach any radio equipments around the mobile station except radio equipments close to the mobile station. When a radio equipment not close to the mobile station calls in this state, the mobile station tries to reply to the calling radio equipment because the input receiver coverage of the mobile station is kept as it is. The output of the mobile station is however low, so that the radio wave cannot reach the calling radio equipment. Communication with calling the radio equipment is ceased and new linkage cannot be established. Furthermore, there is a disadvantage that normal communication is disabled because the mobile station does nothing but repeat replying.
In addition, in an environment in which a plurality of mobile stations generate a queue for a radio equipment which is a base station, for example, in a vending machine (base station) providing service on the basis of requests from radio equipments (mobile stations), the forefront of the queue, that is, the first radio equipment as a party to be serviced cannot be identified and priority cannot be distinguished between radio equipments registered as the queue.